Rubber composition usable in the vulcanized state as a tire safety support and such a support

ABSTRACT

The present invention provides a rubber composition which when vulcanized may be used to form a safety support intended to be mounted on a wheel rim within a tire. The invention also is directed to such a support, capable of supporting a tread of the tire in the event of a drop in inflation pressure, and to a mounted assembly comprising this support. A rubber composition according to the invention comprises (phr: parts by weight per 100 parts of diene elastomer(s)): (a) a diene elastomer, (b) particles of an α-olefinic thermoplastic polymer having a melting point greater than or equal to 150° C., in an amount of 5 to 30 parts by weight per 100 parts diene elastomer (phr), wherein the mean size by weight of the particles is between 50 μm and 500 μm, (c) greater than 60 phr of reinforcing filler, and (d) from 3 to 8 phr of sulphur.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a rubber composition that, inits vulcanized state, may be used in a safety support intended to bemounted on a wheel rim within a tire. The invention is also directed tothe safety support, which is capable of supporting a tread of the tirein the event of a drop in inflation pressure and to a mounted assemblycomprising the support.

[0002] Safety supports for vehicle tires are intended to be mounted on arim within the tire for the purpose of supporting the tread of the tirein the event of a loss of inflation pressure. Such supports comprise abase which is intended to conform to the rim and a crown which isintended to come into contact with the tread in the event of loss ofinflation pressure, but leaves a clearance relative thereto at nominalpressure.

[0003] Japanese patent specification JP-A-3/82601 discloses a safetysupport comprising a substantially cylindrical base and crown, whichfurther comprises an annular body connecting the base and crown.

[0004] This annular body comprises a supporting element which iscontinuous circumferentially having:

[0005] a plurality of partitions extending axially on each side of acircumferential median plane and distributed around the circumference ofthe support, and

[0006] joining elements extending substantially circumferentially, eachjoining element connecting the respective ends of two adjacentpartitions which are arranged on the same side of the support, saidjoining elements being arranged alternately in succession on each sideof said partitions;

[0007] in which the partitions and joining elements are substantiallyrectilinear and the difference between the maximum and minimum values ofthe area of an axial section of the support element as a function of theazimuth, relative to the sum of these same areas, is preferably lessthan 0.3. As a consequence, as a function of the azimuth, the area of anaxial section of the support element varies at most by a factor of twoin order to ensure good uniformity of loading capacity and to limitvibration when running on the support.

[0008] This support is produced from a hard polymeric material, with thewhole supporting element being designed to withstand compressive loads.

[0009] Such supports may be produced in conventional manner, for exampleby injection molding.

[0010] Vulcanized rubber compositions intended to constitute part of atire and which exhibit improved rigidity characteristics are also known;See, e.g., U.S. Pat. No. 5,023,301 which discloses compositions thatcomprise an elastomer matrix in which polypropylene fibrils of a maximumlength of 15 μm and a reinforcing filler are randomly dispersed.

[0011] One major disadvantage of the composition is its reducedelongation at break in comparison with a “control” composition notcontaining polypropylene fibrils (the ultimate elongation modulus isless than one third of the corresponding modulus of the “control”composition). Such compositions, therefore, are not suitable forconstituting safety supports.

SUMMARY OF THE INVENTION

[0012] The object of the present invention is to provide a rubbercomposition, which in its vulcanized state can be used in a safetysupport intended to be mounted on a wheel rim inside a tire. Thecomposition is such that it provides for improved weight reductionperformance for the support over known supports at a comparable flatrunning service life.

[0013] The rubber composition according to the invention comprises (inparts by weight per 100 parts of diene elastomer(s)):

[0014] at least one diene elastomer,

[0015] particles of an α-olefinic thermoplastic polymer, having amelting point greater than or equal to 150° C., in an amount of from 5to 30 phr, wherein the mean particle size by weight of particles isbetween 30 μm and 500 μm,

[0016] more than 60 phr of a reinforcing filler and

[0017] from 3 to 8 phr of sulphur.

[0018] Both the non-vulcanized and the vulcanized rubber compositionsare contemplated in the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention can be better understood with reference tothe appended drawings in which:

[0020]FIG. 1 is a side view of a safety support according to oneembodiment of the invention;

[0021]FIG. 2 is an axial section of a mounted assembly according to theinvention, in which the support of FIG. 1 is mounted on a wheel rim andis in supporting position against a tire;

[0022]FIG. 3 is a section along line AA in FIG. 1 of a supportingelement according to a first embodiment of the invention;

[0023]FIG. 4 is a section along line AA in FIG. 1 of a supportingelement according to a second embodiment of the invention whichcomprises partitions connected together by alternate circumferentialjoining elements;

[0024]FIG. 5, similar to FIG. 4, is a section along line AA in FIG. 1 ofa supporting element, the partitions of which are of variable thickness;

[0025]FIG. 6, similar to FIG. 4, is a section along line AA in FIG. 1 ofa supporting element, the partitions of which comprise a centralconnecting portion which is oriented circumferentially;

[0026]FIG. 7, similar to FIG. 4, is a section along line AA in FIG. 1 ofa supporting element, the circumferential joining elements of which areof variable length;

[0027]FIG. 8, similar to FIG. 4, is a section along line AA in FIG. 1 ofa supporting element, the partitions of which exhibit three reversals ofcurvature across the width thereof;

[0028]FIG. 9, similar to FIG. 4, is a section along line AA in FIG. 1 ofan annular body including another embodiment of a supporting element,the partitions of which exhibit three reversals of curvature across thewidth thereof;

[0029]FIGS. 10 and 11, similar to FIG. 4, are respectively sectionsaccording to line AA in FIG. 1 of annular bodies according to theinvention including supporting elements, the partitions of which are ofvariable thickness and having axial supporting walls;

[0030]FIG. 12 is a side view of a support according to said secondembodiment of the invention, the annular body of which comprises acentral web; and

[0031]FIG. 13 is a perspective view illustrating a known supportarchitecture.

DETAILED DESCRIPTION OF THE INVENTION

[0032] In accordance with the invention, a diene elastomer is defined asan elastomer obtained at least in part (i.e. a homopolymer or copolymer)from diene monomers (conjugated or unconjugated monomers bearing twodouble carbon-carbon bonds). One or more elastomers may be used in therubber compositions of the invention.

[0033] Preferably, the elastomers comprise at least one essentiallyunsaturated diene elastomer, which is a diene elastomer is a dieneelastomer which is obtained at least in part from conjugated dienemonomers having a content of moieties or units of diene origin(conjugated dienes) which is greater than 15% (mol %) and includes:

[0034] a) any homopolymer obtained by polymerization of a conjugateddiene monomer, such as 1,3-butadiene, 2-methyl-1,3-butadiene (orisoprene), a 2,3-di(C1 to C5 alkyl)-1,3-butadiene, such as2,3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-butadiene, 2-methyl-3 -isopropyl-1,3 -butadiene, andphenyl-1,3-butadiene;

[0035] b) any copolymer obtained by copolymerization of one or moreconjugated dienes with each other or with one or more vinyl aromaticcompounds, such as styrene, ortho-, para- or meta-methylstyrene.Exemplary copolymers include butadiene-styrene copolymers andbutadiene-isoprene copolymers.

[0036] According to one embodiment of the invention, the rubbercomposition further comprises a homopolymer obtained by polymerizationof a conjugated diene monomer having 4 to 12 carbon atoms, or acopolymer obtained by copolymerization of one or more conjugated dieneswith each other or with one or more vinyl aromatic compounds having from8 to 20 carbon atoms, in a quantity of less than or equal to 40 phr.

[0037] A composition according to the invention may comprise a blend ofapproximately 60 phr of natural rubber and approximately 40 phr ofpolybutadiene.

[0038] The reinforcing filler of the rubber composition according to theinvention preferably comprises a reinforcing white filler in a majorityproportion, i.e. in a mass fraction of greater than 50% of totalreinforcing filler.

[0039] A reinforcing white filler is defined as a white filler which iscapable, on its own, without any intermediate means other than a whitefiller/elastomer bonding agent, of reinforcing a rubber compositionintended for the manufacture of tires. A reinforcing white filler canreplace the reinforcement action of a conventional filler of tire-gradecarbon black.

[0040] Reinforcing white fillers include silica in an amount in thecomposition of greater than 60 phr, advantageously between 60 and 80phr. More preferably, the silica is present in an amount between 65 and75 phr.

[0041] Suitable silicas include any precipitated or pyrogenic silicasknown to those skilled in the art, the BET or CTAB surface area valuesof which are both within a range from 50 m²/g to 200 m²/g. Highlydispersible precipitated silicas are preferred.

[0042] “Highly dispersible silica” is defined as any silica having avery substantial ability to disagglomerate and to disperse in anelastomeric matrix, which can be observed in known manner by electron oroptical microscopy on thin sections. Non-limiting examples of suchhighly dispersible silicas that may be used in the compositions of theinvention include silicas BV 3370 and BV 3380 from Degussa, silicasZeosil 1165 MP and 1115 MP from Rhodia, silica BXR 160 from PPG orsilica Zeopol 8745 M from Huber.

[0043] Preferably, the BET or CTAB surface area values of the silica areboth in the range of between 110 and 200 m²/g and, more preferably,between 140 and 195 m²/g.

[0044] The physical state of the silica may be in the form of a powder,microbeads, granules, balls, etc.

[0045] As used herein, silica includes blends of different silicas.Silica may be used alone or in the presence of other white fillers. TheCTAB specific surface area value is determined in accordance with themethod of Standard NFT 45007 of November 1987. The BET specific surfacearea value is determined in accordance with the method of BRUNAUER,EMMETT and TELLER, which is described in “The Journal of the AmericanChemical Society, vol. 60, p. 309 (1938)” and corresponds to StandardNFT 45007 of November 1987.

[0046] Other non-limiting examples of reinforcing white fillers whichmay be used include:

[0047] aluminas (of the formula Al₂O₃), such as the high dispersibilityaluminas, described in European Patent Specification EP-A-810 258 and

[0048] aluminium hydroxides, such as those disclosed in internationalpatent specification WO-A-99/28376.

[0049] The reinforcing filler in the composition of the invention mayalso comprise grade 6 or grade 7 carbon black in a minority proportion,i.e. in a mass fraction of less than 50% of the reinforcing filler.Carbon blacks N683 and N772 are suitable for this purpose.

[0050] Carbon black/silica blends or carbon blacks partially or entirelycoated with silica are also suitable as a reinforcing filler accordingto the invention.

[0051] The rubber composition of the invention also comprises, areinforcing white filler/elastomer bonding agent (also known as acoupling agent) when the reinforcing filler comprises a reinforcingwhite filler. The purpose of the bonding agent is to provide an adequatechemical and/or physical bond (coupling) between the white filler andthe elasiomer(s) while facilitating dispersion of the white fillerwithin the elastomeric matrix.

[0052] The bonding agent, which is at least bifunctional, has thesimplified general formula “Y-T-X”, in which:

[0053] Y represents a functional group (“Y” function) which is capableof bonding physically and/or chemically with the white filler, the bondbeing established, for example, between a silicon atom of the couplingagent and the hydroxyl (OH) surface groups of the filler (for example,surface silanols in the case of silica);

[0054] X represents a functional group (“X” function) which is capableof bonding physically and/or chemically with the elastomer, for exampleby means of a sulphur atom; and

[0055] T represents a hydrocarbon group that links Y and X.

[0056] These bonding agents are not to be confused with simple agentsfor coating the filler. Such simple agents may comprise the Y functionwhich is active with respect to the filler, but are devoid of the Xfunction which is active with respect to the elastomer.

[0057] Bonding agents, of variable effectiveness, have been described ina large number of documents and are well-known to those skilled in theart. In fact, any bonding agent which is known to or likely to ensureeffective bonding between the silica and diene elastomer in rubbercompositions usable in tires, such as organosilanes, in particularpolysulphurized alkoxysilanes or mercaptosilanes, may be used.

[0058] In particular polysulphurized alkoxysilanes are used, such asthose described in U.S. Pat. Nos. 3,842,111, 3,873,489, 3,978,103,3,997,581, 4,002,594 or, more recently, U.S. Pat. Nos. 5,580,919,5,583,245, 5,663,396, 5,684,171, 5,684,172 and 5,696,197.

[0059] So-called “symmetrical” polysulphurized alkoxysilanes whichsatisfy the following general formula (1) are particularly suitable forthe composition, without the definition below being limiting:

Z-A-S_(n)-A-Z, in which:   (I)

[0060] n is an integer from 2 to 8 (preferably from 2 to 5);

[0061] A is a divalent hydrocarbon radical (preferably a C₁-C₁₈ alkyleneor a C₆-C₁₂ arylene, more particularly a C₁-C₁₀ alkylene, in particulara C₂-C₄ alkylene, preferably propylene);

[0062] Z corresponds to one of the formulae below:

[0063] in which:

[0064] R¹, which may or may not be substituted, and may be identical ordifferent, represents a C₁-C₁₈ alkyl, a C₅-C₁₈ cycloalkyl, or a C₆-C₁₈aryl (preferably a C₁-C₆ alkyl, a cyclohexyl or phenyl, in particular aC₁-C₄ alkyl, more particularly methyl and/or ethyl);

[0065] R², which may or may not be substituted, and may be identical ordifferent, represents a C₁-C₁₈ alkoxyl or C₁-C₁₈ cycloalkoxyl(preferably a C₁-C₈ alkoxyl or a C₅-C₈ cycloalkoxyl, more particularlymethoxyl and/or ethoxyl).

[0066] Where mixtures of polysulphurized alkoxysilanes corresponding toformula (I) above, in particular conventional commercially availablemixtures, are used, it will be understood that the mean value of “n” isa fractional number, preferably varying between 2 and 5.

[0067] Particular polysulphurized alkoxysilanes include polysulphides(in particular tetrasulphides) of bis(alkoxyl(C₁-C₄)silylpropyl),particularly bis(trialkoxyl(C₁-C₄)silylpropyl), more particularlypolysulphides of bis(3-trimethoxysilylpropyl) or ofbis(3-triethoxysilylpropyl). Bis(3 -triethoxysilylpropyl) tetrasulphide,abbreviated TESPT, having the formula [(C₂H₅O)₃Si(CH₂)₃S₂]₂, ispreferably used. TESPT is sold, for example by Degussa under the nameSi69 (or X50S when supported at a content of 50 wt % on carbon black) oralternatively by Witco under the name Silquest A1289.

[0068] The person skilled in the art will be able to adjust the contentof bonding agent in the compositions of the invention, according to theintended application, the elastomer(s) used and the quantity ofreinforcing white filler used. The amount by weight of bonding agent inthe rubber compositions of the invention are within a range from 2 to15% relative to the mass of reinforcing white filler, preferably withina range from 5 to 12%.

[0069] The sulphur content in the composition according to the inventionvaries from 3 to 8 phr, preferably from 4 to 6 phr.

[0070] The rubber compositions according to the invention also contain,in addition to the elastomer(s), reinforcing filler, sulphur and one ormore reinforcing white filler/elastomer bonding agent(s), various otherconstituents and additives usually used in rubber mixtures, such asplasticizers, pigments, antioxidants, vulcanization accelerators,extender oils, and/or one or more agents for coating the reinforcingwhite filler, such as alkoxysilanes, polyols, amines etc.

[0071] According to one embodiment of the invention, the α-olefinicpolymer in the rubber composition is isotactic polypropylene.

[0072] According to another feature of the invention, the α-olefinicpolymer particles dispersed in the elastomer(s) are substantiallyspherical.

[0073] The rubber composition according to the invention exhibits an M10elasticity modulus at 10% deformation which is greater than 10 MPa andis preferably greater than 15 MPa. When it is used in a safety support,the composition preferably exhibits an M10 modulus in the range of 25and 35 MPa.

[0074] The vulcanized rubber composition may be prepared as follows:

[0075] in a first thermomechanical working stage, the elastomer(s),reinforcing filler and α-olefinic polymer in the powder state arekneaded, with the dropping temperature being approximately 155° C.,

[0076] in a second mechanical working stage, a sulphur vulcanizationsystem is added to the mixture obtained at the completion of the firststage, and

[0077] in a third vulcanization stage, the mixture obtained uponcompletion of the second stage is cured.

[0078] The process is carried out such that the operating temperaturesof the three stages are always below the melting temperature of theα-olefinic polymer, such that the polymer is dispersed in theelastomer(s) in the form of substantially spherical particles.

[0079] According to one embodiment of the invention, preparationinvolves:

[0080] in the first stage, kneading at an initial temperaturesubstantially equal to 100° C., then

[0081] in the second stage, adding the vulcanization system at atemperature of below 100° C., then

[0082] in the third stage, curing at a temperature substantially equalto 150° C.

[0083] A safety support according to the invention comprises avulcanized rubber composition of the invention. This support comprises:

[0084] a substantially cylindrical base, intended to conform to the rim,

[0085] a substantially cylindrical crown intended to come into contactwith the tire tread in the event of a drop in inflation pressure, but toleave a clearance relative to said tread at nominal inflation pressure,and

[0086] an annular body connecting the base to the crown, the bodycomprising a circumferentially continuous supporting element having acircumferential median plane, the supporting element comprising aplurality of partitions extending axially on each side of thecircumferential median plane and distributed around the circumference ofthe support.

[0087] According to a first embodiment of a support according to theinvention, the annular body also comprises joining elements extendingsubstantially circumferentially on one of the sides of the support, eachjoining element connecting the respective ends of two adjacentpartitions which are arranged on the side of the support, said joiningelements being arranged alternately in succession on each side of saidpartitions.

[0088] In this first embodiment, the joining elements are mutuallysupported between two adjacent partitions by a rib extending from thecrown to the base of the support such that the joining elements form acontinuous joining wall in the form of a gusset all along the side ofthe support.

[0089] More precisely, the joining wall comprises a plurality of cells,each of which is delimited by two adjacent ribs, the bottom of each cellsubstantially exhibiting a dihedral shape, the ridge of which is formedby one of said partitions and the faces of which are respectively formedby the alternate joining elements.

[0090] According to a second embodiment of a support according to theinvention, the annular body also comprises joining elements extendingsubstantially circumferentially on both sides of the support, eachjoining element connecting the respective ends of two adjacentpartitions which are arranged on the same side of the support, thejoining elements being arranged alternately in succession on each sideof said partitions.

[0091] In this second embodiment, the partitions are modified in theircentral portion relative to their lateral ends, so as to increase thebuckling resistance of the annular body under radial load.

[0092] In fact, the central portion of the supporting element is movedaway from the joining elements and may be destroyed during running onthe support by the occurrence of a repeated buckling deformation. In thecase of supports manufactured from an elastomeric material, suchrepeated buckling deformation during running initiates and propagatescracking on the side of the walls subjected to extension. On the otherhand, in the case of supports manufactured from plastic materials,buckling deformation results in plastic deformation. Such irreversibledeformation considerably reduces the stiffness and the loading capacityof the structure, progressively rendering it incapable of fulfilling itsfunction.

[0093] The ratio between the thickness of the partitions in theircentral portion and in their lateral ends is greater than 1.1 andpreferably greater than 1.5. The variation in thickness substantiallyincreases the buckling resistance of the central portion of thepartitions, which means that, for a given radial load, the thickness ofthe joining elements may be limited and the total weight of the supportmay be reduced.

[0094] From one lateral end to the other, these partitions exhibit atleast one reversal and, preferably, three reversals in the direction ofthe curvature thereof.

[0095] These partitions exhibit, for example, a central portionextending substantially axially between two lateral portions, theselateral portions meeting the joining elements and forming an angle γrelative to the circumferential direction ranging from 20 to 40 degrees.

[0096] According to another embodiment of a support of the invention,the partitions exhibit, in their central zone, two portions extendingsubstantially axially and offset circumferentially relative to eachother, together with a third joining portion. The mean variation α inorientation between the third joining portion and the two substantiallyaxially oriented portions is preferably greater than 20 degrees.

[0097] Each joining element may be supported on only one side or on bothsides of the supporting element by at least one wall extendingsubstantially axially towards the outside of the annular body.

[0098] These axial walls are relatively insensitive to buckling becausethey are integral with the supporting element and relatively short. At agiven constant width of the support, these axial walls make it possibleto reduce the width of the supporting element and thus to increase thebuckling resistance thereof.

[0099] In a preferred embodiment, a three-branched star structure isformed from each joining element with a supporting axial wall and thelateral ends of the two adjacent partitions, the axial width of oneaxial wall being less than or equal to half the axial width of the twoadjacent partitions of the supporting element.

[0100] The supporting elements according to the invention may alsocomprise a web which is substantially cylindrical and coaxial with thesupport, such web being, for example, arranged radially at half heightof the supporting element. This web is made from the same material asthe rest of the annular body. When arranged at half height, the weballows the height of the partitions to be divided by two, therebyapproximately quadrupling the limit buckling load.

[0101] In order to facilitate manufacture of the supports according tothe invention, the various geometries of the supporting elements areadjusted so as to comprise no undercut portions obstructing axialdemolding of the support.

[0102] Preferably, a mounted assembly according to the invention for amotor vehicle comprises a wheel rim, a tire mounted on the rim and thesupport according to the invention. The rim comprises on each of theperipheral edges thereof a rim seat intended to receive a bead of thetire, the rim therefore having two seats. The rim comprises between thetwo seats, a bearing surface and a mounting groove connecting thebearing surface to an axially internal lip of one of the seats, or firstseat.

[0103] It will be noted that the flat structure which is imparted tosaid rim by the bearing surface is such that, during flat running, theentire width of the support bears the load, unlike “hollow” type rims.

[0104] The aforementioned characteristics of the present invention, aswell as others, will be better understood on reading the followingdescription of several embodiments of the invention, which are given byway of illustration and not of limitation in comparison with otherexamples not according to the invention.

[0105] The above-stated embodiments relating to examples of architectureof the support according to the invention are moreover illustrated bythe attached drawings, which are discussed in detail below.

[0106] In the following examples, flat running tests were performed onsupports according to the invention and “control” supports which differin regard to the composition of the rubber from which they are made andby the selected architecture for these supports.

[0107] Referring to FIGS. 1 and 2, each of supports 1 essentially havethree parts:

[0108] a base 2, of generally annular shape;

[0109] a substantially annular crown 3, optionally having longitudinalgrooves 5 on the radially external wall thereof, and

[0110] an annular body 4 connecting base 2 and crown 3.

[0111]FIG. 2 illustrates the function of support 1, namely supportingthe tire tread in the event of severe loss of inflation pressure of thetire.

[0112] Each tested support was incorporated into a mounted assemblyintended to equip a motor vehicle sold under the name “PEUGEOT 806”.

[0113] The rim used for this mounted assembly was as is shown in FIG. 2,which is described above with reference to the preferred mountedassembly of the invention. (This rim is also described in detail inFrench patent specification FR-A-2 720 977.)

[0114] More precisely, the characteristic dimensions (tire width, tirediameter, rim diameter, respectively) of each mounted assembly which wastested are, in mm:

[0115] 205-650-440.

[0116] The characteristic dimensions (width, internal diameter, height,respectively) in mm of each support which was tested are 135-440-50.

[0117] For each flat running test (controls and supports according tothe invention), care was taken to ensure that the same relative crushingof the support in the radial direction thereof was obtained (thisconstant relative crushing being defined as the ratio of deflection tothe height of the support).

[0118] The running conditions for each of the tests were as follows:load on wheel: 530 kg; running speed: 100 km/h; running temperature:between 20° C. and 25° C. running on a motorway type circuit.

CONTROL EXAMPLES 1) Control Example 1

[0119] A first control support which was incorporated into theabove-described mounted assembly for the purposes of the flat runningtest was manufactured from a vulcanized rubber composition as definedbelow: elastomer: natural rubber 100 phr; reinforcing filler: “ZEOSIL1165 MP” silica  54 phr

[0120] (silica sold by Rhodia exhibiting BET and CTAB surface areavalues of at least 150 to 160 m²/g); coupling agent: Si69/carbon blackN330 8.5 phr*   “6PPD”: 2 phr; ZnO: 4 phr; stearic acid: 1 phr;vulcanization accelerator: “CBS”: 3 phr; sulphur: 4.5 phr;  

[0121] where “6PPD” isN-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine and “CBS” isN-cyclohexylbenzothiazyl sulphenamide.

[0122] This first control support exhibits an M10 elasticity modulus of9 MPa (M10 being the standard abbreviation for a secant elongationmodulus obtained at a deformation of approx. 10%, at room temperatureand on the third loading cycle, in accordance with Standard ISO37-1977).

[0123] This support is of a known architecture, which is shown in FIG.13, in relation to FIGS. 1 and 2.

[0124] The section of FIG. 2 shows a first solid portion 4 a of annularbody 4 together with a second portion 4 b having recesses (c.f. alsoFIG. 1) extending axially over substantially more than half of annularbody 4 and opening on the outside in a substantially axial direction.Recesses 4 b are distributed regularly around the entire circumferenceof annular body 4 and they define partitions 6, which provide a directradial connection between crown 2 and base 3 of support 1.

[0125] This geometry has the advantage of subjecting partitions 6 toflexural rather than compressive loads when the partitions are crushed.Recesses 4 b and, thus, partitions 6 are sufficient in number to ensureregular support during running on the support.

[0126] More precisely, this first control support 1 which was testedcomprises, around its circumference, 38 partitions 6, each of whichexhibits a thickness of 18 mm, which are spaced two by two at a distanceof 38 mm.

[0127] Furthermore, base 2 and crown 3 exhibit a thickness of 7 mm and 8mm, respectively. The annular body of first control support 1 exhibits,in the axial direction, a thickness of 35 mm.

[0128] The mass of this first control support is 8 kg.

[0129] The results of the running test conducted under the above-statedconditions for the mounted assembly comprising this first controlsupport revealed a service life of greater than 200 km.

2) Control Example 2

[0130] A second control support which was incorporated into theabove-described mounted assembly for the purposes of the flat runningtest was manufactured from a vulcanized rubber composition which differsfrom that of the first control support in that it comprises a blend ofnatural rubber (60 phr) and polybutadiene (40 phr). The architecture,dimensions and mass of this support were identical to those of saidfirst control support.

[0131] This second control support exhibited substantially identical M10modulus values relative to the first control support.

[0132] The results of the running test carried out under theabove-stated conditions for this mounted assembly comprising this secondcontrol support also revealed a service life of greater than 200 km.

[0133] Testing was also performed on other control supports manufacturedfrom control compositions according to control examples 1 or 2, butwhich exhibit an architecture as described below with reference to FIGS.3 to 12. The results of the running test carried out under theabove-stated conditions revealed a service life for these supports ofless than 100 km.

Examples of Supports According to the Invention

[0134] A series of supports according to the invention was tested. Allof the supports were manufactured from the same vulcanized rubbercomposition and exhibited the architectures illustrated in FIGS. 3 to12, respectively.

[0135] For the sake of clarity in the present description, the testedsupport architectures are presented at the end of the description.

[0136] Each support according to the invention was manufactured usingthe vulcanized rubber composition as follows: elastomer: natural rubber100 phr;  reinforcing filler: “ZEOSIL 1165 MP” silica 70 phr;  couplingagent: Si69/carbon black N330 11 phr;* isotactic polypropylene: 10 phr; “6PPD”: 2 phr; ZnO: 4 phr; stearic acid: 1 phr; vulcanizationaccelerator: “CBS”: 3 phr; sulphur: 4.5 phr;  

[0137] This vulcanized rubber composition is prepared as follows:

[0138] In a first thermomechanical working stage performed in a 6 literinternal mixer, all the necessary constituents, including the couplingsystem and various additives, with the exception of the vulcanizationsystem, are kneaded. The elastomer, reinforcing filler and polypropyleneare mixed in the powder state at an initial temperature of 100° C.(elastomer feed temperature), such that the polypropylene is dispersedin the elastomer, with the dropping temperature being approximately 155°C.

[0139] In a second mechanical working stage carried out at a temperatureof below 100° C., the sulphur vulcanization system is added to themixture obtained on completion of the first stage.

[0140] In a third vulcanization stage, the mixture obtained oncompletion of the second stage is cured at a temperature of 150° C.

[0141] Performing these three stages at temperatures below the meltingpoint of polypropylene (168° C.) makes it possible to obtain adispersion of non-fibrillated particles of polypropylene in theelastomer. More precisely, these non-fibrillated particles exhibit asubstantially spherical shape.

[0142] A sieving method was used to determine the particle sizedistribution of the polypropylene powder introduced into the mixer bymeasuring, for a given initial mass of polypropylene, the proportion ofoversize particles on successive passage through the sieves. This methodwas performed in accordance with Standards ISO-1435 and NF-14001.

[0143] This particle size distribution was as follows for each sieve,stated in cumulative mass fractions relative to the initial mass ofpolypropylene: size <45 μm; 0.09% size <125 μm;  5.9% size <180 μm;11.4% size <315 μm; 38.3% size <400 μm; 73.9% size <500 μm; 99.9% size<630 μm;  100%.

[0144] On this basis, it was concluded that the mean size by weight ofthe particles in the rubber composition according to the invention isbetween 50 μm and 500 μm.

[0145] Advantageously, each support according to the invention has amass of 5 kg, which is approximately one third less than the 8 kg massof each of the control supports. Thus, each support according to theinvention exhibits a reduced mass relative to the said “control”supports.

[0146] Furthermore, the results of the running test carried out underthe above-stated conditions for mounted assemblies comprising supportsaccording to the invention also revealed a service life of greater than200 km.

[0147] Each support according to the invention exhibits an M10 modulusof approximately 30 MPa, which imparts thereto a rigidity greater thanthat of supports not containing the dispersion.

[0148] Moreover, the reinforcing white filler, (silica), in the aboverubber composition used for each support according to the inventionimparts to the composition improved uncured processing characteristics,as well as improved cured properties, such as cohesion, in addition tothe above-mentioned rigidity.

Architectures Tested in Each Case for the Supports According to theInvention

[0149] A first preferred architecture of the support according to theinvention is illustrated in FIG. 3.

[0150] As has been stated above in general terms, with reference toFIGS. 1 and 2, a safety support 1 with the architecture depicted in FIG.3 comprises base 2, crown 3 and annular body 4.

[0151]FIG. 3 shows a circumferentially continuous supporting element 7of preferred support 1, the supporting element comprising a plurality ofpartitions 6 extending axially on each side of the circumferentialmedian plane P of support 1 and being distributed around thecircumference of support 1.

[0152] It may be seen in FIG. 3 that supporting element 7 comprises, onone of the sides of support 1, joining elements 8 extendingsubstantially circumferentially. Each joining element 8 connects therespective ends 6 a of two adjacent partitions 6 which are arranged onsaid side of support 1, the joining elements 8 being arrangedalternately in succession on each side of partitions 6.

[0153] More precisely, joining elements 8 are mutually supported betweentwo adjacent partitions 6 by a rib 8 a extending from crown 3 to base 2of support 1, such that joining elements 8 form a continuous joiningwall 9 in the form of a gusset all along the side of support 1.

[0154] More precisely, joining wall 9 comprises a plurality of cells 9a, each delimited by two adjacent ribs 8 a. The bottom of each cell 9 aexhibits a substantially dihedral shape, the ridge of which is formed byone end 6 a of partition 6 and the faces of which are respectivelyformed by alternate joining elements 8.

[0155] There are 40 partitions 6 of support 1 around the circumferenceof support 1 in this tested example. Each partition exhibits a thicknessof 8 mm and they are 40 mm apart. As stated above, each support 1 thatwas tested exhibits a width of 135 mm, a diameter of 440 mm and a heightof 50 mm.

[0156] Base 2 and crown 3 of support 1 exhibit a thickness of 6 mm and 7mm, respectively.

[0157] The distance in the axial direction between a plane P′ in FIG. 3,which is axially median for joining elements 8, and the respective freeends of ribs 8 a, is 20 mm for this example.

[0158] A second architecture of support 1 according to the invention isillustrated in FIG. 4, with FIGS. 5 to 12 illustrating variants of thissecond design (the structural elements analogous to those of FIG. 4 arehereinafter identified by reference numerals incremented by 10 for eachFig., starting from FIG. 5).

[0159] Supports 1 relating to these FIGS. 4 to 12 all comprise base 2,crown 3 and an annular body 10.

[0160]FIG. 4 depicts an annular body 10 consisting of acircumferentially continuous supporting element 11 which comprises a setof partitions 12 connected two by two by joining elements 13.

[0161] Partitions 12 extend laterally on each side of thecircumferential median plane P of support 1 and they are regularlydistributed around the circumference of support 1. They have an angle ofinclination Δ, relative to the circumferential direction, whichapproaches 90 degrees. The thickness H thereof is constant. Moreover,two adjacent partitions 12 have an opposing angle of inclinationrelative to the axial direction.

[0162] Joining elements 13 have a thickness e and are orientedcircumferentially. Each joining element 13 connects the respective endsof two adjacent partitions 12 which are arranged on the same side ofsupport 1 (these two ends are the ones closest to each other). Joiningelements 13 are thus arranged alternately in succession on each side ofpartitions 12.

[0163] It will be noted that, in order to facilitate manufacture ofsupport 1 using axial demolding, supporting element 11 comprises noundercut elements.

[0164]FIG. 5 shows a variant embodiment of supporting element 21(compare to supporting element 11 of FIG. 4).

[0165] Partitions 22 of supporting element 21 have a thickness H intheir central portion which is greater than the thickness h thereof attheir lateral ends. In this example, H is approximately twice the sizeof h.

[0166] This variation in thickness imparts very good buckling resistanceto the central portions of partitions 22. The lateral ends are connectedto joining elements 23 in continuous manner, which imparts good bucklingresistance thereto.

[0167] It will be noted that a variation in thickness of as little as10% may have appreciable effects for the purpose of postponing the onsetof overload buckling.

[0168]FIG. 6 shows another variant embodiment, supporting element 31.

[0169] As above, supporting element 31 comprises partitions 32 which areconnected by joining elements 33. Partitions 32 comprise two lateralportions 34 having the same angle of inclination Δ, relative to thecircumferential direction, which are offset circumferentially and areconnected in the central portion of supporting element 31 by a thirdportion 35 oriented substantially circumferentially.

[0170] The mean variation α in orientation between lateral portions 34and central portion 35 is of the order of 80 degrees in this case. Sinceportions 35 are oriented circumferentially, angles α and Δ are equal.

[0171] This presence of this third central portion 35, which has a meanorientation differing greatly from that of the two lateral portions,increases the buckling resistance of the central portion of thepartitions 32.

[0172] It will be noted that, in order to be effective, variation a mustbe greater than 20 degrees.

[0173] In this embodiment, partitions 32 comprise, from one lateral endto the other, one reversal in the direction of the curvature thereof.

[0174]FIG. 7 shows another variant embodiment, supporting element 41.

[0175] In this case, joining elements 43, which are arranged on one sideof supporting element 41, have a circumferential length which is lessthan that of joining elements 44, which are arranged on the other sideof supporting element 41.

[0176] It will be noted that the substantially doubled length of joiningelements 44 increases the compressive stiffness of supporting element 41on this side of the support 1. This latter side should be arrangedtowards the interior side of the vehicle, where the loads borne bysupport 1, while in operation, are the greatest.

[0177]FIG. 8 shows another variant embodiment, supporting element 51.

[0178] In this case, joining elements 53 are virtually reduced to thecontact surface between two lateral ends 54 as an arc of a circle ofpartitions 52.

[0179] Partitions 52 also comprise a central connecting portion 55.

[0180] It will be noted that variation α in mean orientation between thetwo lateral portions 56 and central portion 55 is greater than 90degrees and is of the order of 110 degrees, which increases the meansupporting density of supporting element 51 in the central portionthereof.

[0181] From one lateral end to the other, partitions 52 comprise threereversals in the direction of the curvature thereof.

[0182]FIG. 9 shows another variant embodiment, supporting element 61, avariant similar to that shown in FIG. 8 with the followingmodifications.

[0183] Partitions 62 comprise rectilinear segments and exhibit threereversals in the direction of the curvature thereof. The partitionscomprise two axially oriented lateral portions 64, which are connected,on the one hand, by central portion 65 and, on the other hand, tojoining elements 63 by lateral ends 66 having a mean orientation γapproaching 30 degrees, relative to the circumferential direction.

[0184] Mean variation α in orientation between the two axially orientedportions 64 of partitions 62 and central joining portion 65 is of theorder of 40 degrees.

[0185] Joining elements 63 may be defined as elements of a substantiallytriangular cross-section, which are arranged between two adjacentlateral ends 66.

[0186] On both sides of supporting element 61, annular body 60 comprisesa series of substantially axially oriented walls 67 which extend eachjoining element 63 towards the outside of support 1. As may be seen inFIG. 9, a three-branched star, which is highly resistant to buckling, isformed where each joining element 63, adjacent lateral ends 66 and axialwall 67 meet.

[0187]FIG. 10 shows another variant embodiment, annular body 70 andsupporting element 71.

[0188] Supporting element 71 comprises partitions 72 having axiallyoriented central portions 74 which are extended on each side by lateralend 75, which exhibits orientation γ approaching 30 degrees relative tothe circumferential direction.

[0189] On one side of annular body 70, joining elements 73 are reducedto the contact surface between two adjacent lateral ends 75. On theother side, annular body 70 comprises lateral walls 76 which supportjoining elements 77 on this side, the joining elements being of asubstantially triangular shape.

[0190] It will be noted that on this latter side, the compressivestiffness of the supporting element is greater.

[0191] The length of lateral walls 76 is, in particular, less than halfthe length of central portions 74 of partitions 72, so that they are notliable to buckle.

[0192] The side of supporting element 71 having the highest radialcompressive stiffness should preferably be arranged on the interior sideof the vehicle. It has, in fact, been observed that the loads arehighest on this interior side of the vehicle.

[0193] Partitions 72 have a thickness H in their central portion 74which is greater than thickness h of their lateral portions 75, so as toincrease the buckling resistance of central portion 74.

[0194]FIG. 11 shows another variant embodiment, annular body 80, avariant very similar to annular body 70 of FIG. 10.

[0195] Annular body 80 comprises axial lateral walls 86 and 87 whichsupport supporting element 81 on both sides the supporting element 81also being structurally similar to supporting element 71 of FIG. 10.

[0196] For a given width of annular body 80, lateral walls 86 and 87exhibit the advantage of reducing the axial width of partitions 82 ofcontinuous supporting element 81 and thus of improving the bucklingresistance of the overall structure. The axial lengths of walls 86 and87 may differ, as illustrated in FIG. 11.

[0197]FIG. 12 shows an axial view of a support 1 including a supportingelement 91, analogous to the supporting element of FIG. 1, butadditionally comprising circumferential web 94, which is arranged athalf height of annular body 90. Circumferential web 94, of cylindricalshape, provides the advantage of bringing about a very substantialincrease, of the order of a factor of four, in the limit buckling loadof the structure of support 1.

[0198] Each of the supports 1 described with reference to FIGS. 4 to 12exhibits the following dimensional characteristics.

[0199] There are 40 partitions (designated 12 . . . 92 in FIGS. 4 to 12,respectively) around the circumference of each support 1. Each partitionexhibits a thickness of 8 mm and they are 40 mm apart. As stated above,each tested support 1 exhibits a width of 135 mm, a diameter of 440 mmand a height of 50 mm.

[0200] Furthermore, base 2 and crown 3 of support 1 exhibit a thicknessof 6 mm and 7 mm, respectively.

[0201] All supporting elements (designated 7, 11 . . . 91 in theFigures) and annular bodies (designated 4, 10 . . . 90 in the Figures)may be manufactured from the vulcanized rubber composition of theinvention by molding techniques. In order to facilitate axial demolding,they preferably comprise no undercut portions.

[0202] It will be noted that it would also be possible to use, as asupport architecture according to the invention, a support having two ormore rings connected together in the axial direction of the support, theoverall structure thereof remaining unchanged.

[0203] It could, for example, be possible to provide for such a supporta first ring having a substantially rectangular axial section, and oneor more annular elements comprising a plurality of recesses andextending substantially axially across the entire width thereof anddistributed substantially regularly around the circumference thereof.

[0204] Such a ring-type support is easier to introduce into a tire, dueto the lower flexural rigidity of the various annular elements thereof.

We claim:
 1. A rubber composition which, when vulcanized, is usable in asafety support intended to be mounted on a wheel rim inside a tire, thecomposition comprising: (a) a diene elastomer, (b) particles of anα-olefinic thermoplastic polymer having a melting point greater than orequal to 150° C., inn amount of 5 to 30 parts by weight per 100 partsdiene elastomer (phr), wherein the mean size by weight of the particlesis between 30 μm and 500 μm, (c) greater than 60 phr of reinforcingfiller, and (d) from 3 to 8 phr of sulphur.
 2. The rubber composition ofclaim 1, wherein the reinforcing filler comprises greater than 50%reinforcing white filler.
 3. The rubber composition of claim 2, whereinthe reinforcing white filler is silica in an amount ranging from 60 to80 phr.
 4. The rubber composition of claim 2, further comprising apolysulphurized alkoxysilane reinforcing white filler/elastomer bondingagent.
 5. The rubber composition of claim 1, wherein the α-olefinicpolymer is isotactic polypropylene.
 6. The rubber composition of claim1, wherein the diene elastomer is either natural rubber or syntheticpolyisoprene.
 7. The rubber composition of claim 1, wherein the dieneelastomer is a blend of: (a) natural rubber or synthetic polyisoprene inan amount greater than or equal to 60 phr, and (b) a homopolymerobtained by polymerization of a conjugated diene monomer having from 4to 12 carbon atoms or a copolymer obtained by copolymerization of one ormore conjugated dienes with each other or with one or more vinylaromatic compounds having from 8 to 20 carbon atoms, in an amount ofless than or equal to 40 phr.
 8. The rubber composition of claim 7,wherein the blend comprises approximately 60 phr of natural rubber andapproximately 40 phr of polybutadiene.
 9. The rubber composition ofclaim 1, wherein the composition exhibits an M10 elasticity modulus at10% deformation which is greater than 10 MPa.
 10. The rubber compositionof claim 1, wherein the α-olefinic polymer is dispersed in the elastomerin the form of substantially spherical particles.
 11. A process forpreparing a vulcanized rubber composition comprising: (a) a dieneelastomer, (b) particles of an α-olefinic thermoplastic polymer having amelting point greater than or equal to 150° C., in an amount of 5 to 30parts by weight per 100 parts diene elastomer (phr), wherein the meansize by weight of the particles is between 50 μm and 500 μm, (c) greaterthan 60 phr of reinforcing filler, and (d) from 3 to 8 phr of sulphur,the process comprising: (i) in a first thermomechanical working stage,kneading the elastomer, reinforcing filler and α-olefinic polymer in thepowder state, such that the dropping temperature is approximately 155°C., (ii) in a second mechanical working stage, adding a sulphurvulcanization system to the mixture obtained on completion of stage (i),and (iii) in a third vulcanization stage, curing of the mixture obtainedon completion of stage (ii), wherein the operating temperatures ofstages (i)-(iii) are always below the melting temperature of theα-olefinic polymer, such that the polymer is dispersed in the elastomerin the form of substantially spherical particles.
 12. The process ofclaim 11, wherein stage (i) is carried out at an initial temperaturebelow 100° C., stage (ii) is carried out at a temperature below 100° C.and stage (iii) is carried out at a temperature substantially equal to150° C.
 13. A safety support for mounting on a wheel rim inside avehicle tire, the safety support being capable of supporting a tread ofthe tire in the event of a drop in inflation pressure, wherein thesupport comprises a vulcanized rubber composition comprising: (a) adiene elastomer, (b) particles of an α-olefinic thermoplastic polymerhaving a melting point greater than or equal to 150° C., in an amount of5 to 30 parts by weight per 100 parts diene elastomer (phr), wherein themean size by weight of the particles is between 50 μm and 500 μm, (c)greater than 60 phr of reinforcing filler, and (d) from 3 to 8 phr ofsulphur.
 14. The safety support of claim 13 wherein the supportcomprises: (a) a substantially cylindrical base, intended to conform tothe wheel rim, (b) a substantially cylindrical crown intended to contactthe tire tread in the event of a drop in inflation pressure and to leavea clearance relative to the tread at nominal pressure, and (c) anannular body connecting the base to the crown, the annular bodycomprising a circumferentially continuous supporting element with acircumferential median plane, wherein the supporting element comprises:(i) a plurality of partitions extending axially on each side of thecircumferential median plane and distributed around the circumference ofthe support, and (ii) joining elements extending substantiallycircumferentially on one of the sides of the support, each joiningelement connecting the respective ends of two adjacent partitions whichare arranged on the side of the support, the joining elements beingarranged alternately in succession on each side of the partitions,wherein, between two adjacent partitions, the joining elements aremutually supported by a rib extending from the crown to the base of thesupport, such that the joining elements form a continuous joining wallin the form of a gusset extending along the side of the support.
 15. Thesafety support of claim 14, wherein the continuous wall comprises aplurality of cells, each of which is delimited by two adjacent ribs, thebottom of each cell exhibiting a substantially dihedral shape, the ridgeof which is formed by one of the partitions and the faces of which arerespectively formed by the alternate joining elements.
 16. The safetysupport of claim 13, wherein the support comprises: (a) a substantiallycylindrical base, intended to conform to the wheel rim, (b) asubstantially cylindrical crown intended to contact the tire tread inthe event of a drop in inflation pressure and to leave a clearancerelative to the tread at nominal pressure, and (c) an annular bodyconnecting the base to the crown, the body comprising acircumferentially continuous supporting element with a circumferentialmedian plane, wherein the supporting element comprises: (i) a pluralityof partitions extending axially on each side of the circumferentialmedian plane and distributed around the circumference of the support,and (ii) joining elements extending substantially circumferentially,each joining element connecting the respective ends of two adjacentpartitions which are arranged on the same side of the support, thejoining elements being arranged alternately in succession on each sideof the partitions, wherein the partitions are modified in their centralportion relative to their lateral ends such as to increase bucklingresistance of the annular body under radial load.
 17. The safety supportof claim 16, wherein the ratio between the thickness of the partitionsin their central portion and in their lateral ends is greater than 1.1.18. The safety support according to claim 16, wherein the partitions,from one lateral end to the other, exhibit at least one reversal indirection of the curvature thereof.
 19. The safety support of claim 18,wherein the partitions have a central portion extending substantiallyaxially between two lateral portions, the lateral portions meeting thejoining elements and forming an angle y with the circumferentialdirection ranging from 20 to 40 degrees.
 20. The safety support of claim16, wherein the partitions, from one lateral end to the other, exhibitat least three reversals in direction of the curvature thereof.
 21. Thesafety support of claim 18, wherein the partitions exhibit, in theircentral zone, two portions extending substantially axially and offsetcircumferentially relative to each other, together with a third joiningportion.
 22. The safety support of claim 16, wherein on at least oneside of the supporting element, each joining element is supported by atleast one wall extending substantially axially towards the outside ofthe annular body.
 23. The safety support of claim 22, wherein eachjoining element forms a three-branched star structure with a supportingaxial wall and the lateral ends of the two adjacent partitions.
 24. Thesafety support of claim 16, wherein the supporting element furthercomprises a web which is substantially cylindrical and coaxial with thesupport, the web being arranged radially at half height of thesupporting element.
 25. The safety support of claim 16, wherein thesupporting element contains no undercut portions that may obstruct axialdemolding of the support.
 26. A mounted assembly for a motor vehiclecomprising a wheel rim, a tire mounted on the rim and a safety supportaccording to any one of claims 13 to 25 mounted on the rim inside thetire so as to be capable of supporting a tread of said tire in the eventof a drop in inflation pressure, the rim comprising on each peripheraledge thereof a rim seat intended to receive a bead of the tire, the rimcomprising between the two seats thereof, a bearing surface and amounting groove connecting the bearing surface to an axially internallip of one of the seats, or first seat.